Heavy duty powder detergent compositions for home use fabric laundering generally perform well and are widely accepted. With the increasing trend to cold Water washing of fabrics at wash water temperatures below about 60.degree. F. for energy conservation, commercial laundry detergent compositions tend to leave a cold water residue (CWR) of undissolved detergent solids after completion of the wash machine cycles.
The detergency of powder detergent compositions in fabric laundering applications is directly affected by the hardness of the wash water. Control of water hardness typically is achieved with detergency builders, such as water-soluble sequestering builders, water-insoluble ion exchange builders, and water-soluble precipitating builders.
Sodium carbonate is a preferred detergent builder because of cost considerations, but it has inherent disadvantages. Sodium carbonate alone is not capable of reducing the calcium ion concentration in hard water to a level sufficient to provide high detergency under conventional fabric washing conditions. Also, precipitated calcium carbonate tends to coat undissolved detergent particles.
Particularly in the case of cold water laundering of fabrics, the coating of detergent particles with precipitated calcium carbonate suppresses dissolution of the sodium carbonate ingredient. This results in a substantial loss of detergency building activity, and there is a consequential remainder of a cold water residue of undissolved detergent solids.
Laundry detergent formulations which have been developed for use in cold water washing of fabrics are described in U.S. Pat. Nos. 4,196,095; 4,530,774; and 4,695,284.
There is continuing interest in the development of heavy duty laundry detergents which exhibit improved properties for cold water laundry applications.
Accordingly, it is an object of this invention to provide a powder detergent composition which performs with a minimized amount of residual undissolved detergent solids under cold water fabric laundering conditions.
It is a further object of this invention to provide a process for producing a powder detergent composition which has detergent granules coated with an anionic surfactant ingredient.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.